全文获取类型
收费全文 | 246154篇 |
免费 | 3305篇 |
国内免费 | 739篇 |
专业分类
电工技术 | 4015篇 |
综合类 | 769篇 |
化学工业 | 36075篇 |
金属工艺 | 10816篇 |
机械仪表 | 7850篇 |
建筑科学 | 4807篇 |
矿业工程 | 2548篇 |
能源动力 | 5013篇 |
轻工业 | 14708篇 |
水利工程 | 3466篇 |
石油天然气 | 7774篇 |
武器工业 | 26篇 |
无线电 | 23230篇 |
一般工业技术 | 48371篇 |
冶金工业 | 54330篇 |
原子能技术 | 6793篇 |
自动化技术 | 19607篇 |
出版年
2021年 | 2132篇 |
2019年 | 2045篇 |
2018年 | 4121篇 |
2017年 | 4375篇 |
2016年 | 5026篇 |
2015年 | 2989篇 |
2014年 | 4190篇 |
2013年 | 9127篇 |
2012年 | 7718篇 |
2011年 | 9553篇 |
2010年 | 6488篇 |
2009年 | 7212篇 |
2008年 | 7183篇 |
2007年 | 7097篇 |
2006年 | 6103篇 |
2005年 | 8361篇 |
2004年 | 7145篇 |
2003年 | 6554篇 |
2002年 | 5191篇 |
2001年 | 5198篇 |
2000年 | 4453篇 |
1999年 | 4778篇 |
1998年 | 15830篇 |
1997年 | 10665篇 |
1996年 | 7799篇 |
1995年 | 5483篇 |
1994年 | 4594篇 |
1993年 | 4857篇 |
1992年 | 3197篇 |
1991年 | 3270篇 |
1990年 | 3160篇 |
1989年 | 3096篇 |
1988年 | 3132篇 |
1987年 | 2707篇 |
1986年 | 2743篇 |
1985年 | 2997篇 |
1984年 | 2743篇 |
1983年 | 2626篇 |
1982年 | 2419篇 |
1981年 | 2435篇 |
1980年 | 2532篇 |
1979年 | 2415篇 |
1978年 | 2470篇 |
1977年 | 3070篇 |
1976年 | 4145篇 |
1975年 | 2277篇 |
1974年 | 2104篇 |
1973年 | 2208篇 |
1972年 | 1973篇 |
1971年 | 1799篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. Bennahmias H. B. Radousky T. J. Goodwin R. N. Shelton 《Journal of Electronic Materials》1993,22(10):1189-1193
Magnetic characterization has been performed on the members of the cuprateniobate RBa2Cu2NbO8 (R = Pr, Nd, and La) series and R1.5Ce0.5Sr2Cu2NbO10 (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K.
The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition
is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of
the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting
NdCSCNO, SmCSCNO, and EuCSCNO compounds. 相似文献
992.
993.
Polyarteritis nodosa is a rare disorder and a form of systemic vasculitis. A 48 year-old female was admitted to the hospital because menorrhagia and pelvic pain in February 1993. The patient underwent exploratory laparotomy resulting in a total hysterectomy and bilateral salpingo-oophorectomy for myoma of uterus and a right adnexal cystic mass. Histopathologic examination revealed left ovarian periarteritis nodosa. Further investigation and 9 months follow-up failed to show any systemic involvement. To our knowledge the isolated ovarian polyarteritis nodosa is the first case in the literature. 相似文献
994.
Methods are described for forming coating specimens and testing them in pure bending. The proposed tester gives adequate accuracy in determining the elastic characteristics and strength for thin specimens (up to 0.1 mm) of brittle materials of powder-coating type.Translated from Problemy Prochnosti, No. 3, pp. 94–97, March, 1993. 相似文献
995.
996.
997.
Suggests that it is difficult to get an exact account of gambling behavior in Norway. It appears that gambling behavior in Norway has increased 50% during the observed 5-yr period. Little is known about the prevalence of problematic gambling. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
S Inuzuka T Ueno T Torimura S Tamaki H Sugawara R Sakata N Kusaba M Sata K Tanikawa 《Canadian Metallurgical Quarterly》1997,32(10):1052-1060
BACKGROUND: We examined the relationships among vitronectin (VN), plasminogen activator inhibitor-1 (PAI-1), and transforming growth factor beta 1 (TGF-beta 1) in liver diseases to evaluate the presence of plasmin cascade in human hepatic fibrosis. METHODS: Blood and liver tissues were obtained from 57 patients with liver disease. Plasma VN, PAI-1 antigen, and PAI-1 activity levels were evaluated. Biopsied liver specimens were observed by light and electron microscopy after immunohistochemical staining. Morphometric analysis was performed on these specimens. RESULTS: Plasma VN and PAI-1 activity levels decreased significantly with the progression of hepatic fibrosis and were particularly marked in the liver cirrhosis group. Plasma PAI-1 antigen level increased significantly. The immunolocalization of the active form of TGF-beta became more intense with the progression of hepatic fibrosis, whereas that of the dual-stained positive areas of PAI-1 and VN (PAI-1.VN) decreased. There was a positive correlation between TGF-beta and PAI-1, whereas there was a negative correlation between TGF-beta and PAI-1.VN. Immunoelectron microscopy showed the localization of PAI-1-VN in the extracellular space around the sinusoidal cells or surface of aggregating platelets, TGF-beta mainly in Ito cells, and VN in hepatocytes near the focal necrotic area or fibrous septa. CONCLUSIONS: These findings suggest that VN and PAI-1 are related to the active form of TGF-beta and that it is possible that the plasmin cascade is present in the human liver. 相似文献
999.
1000.
W Pf?rringer 《Canadian Metallurgical Quarterly》1997,135(4):Oa10-Oa11